Stereoselective syntheses of syn 5-[1-hydroxy-2-(2-bromo-phenyl)-ethyl]-5-methyl-5H-furan-2-one and syn 5-[1-hydroxy-2-(2-methoxy-phenyl)-ethyl]-5-methyl-5H-furan-2-one

The aldol condensation of 2-(tert-butyldimethylsilyloxy)-5-methyl-furan 4 with several phenylacetaldehydes led stereoselectively to the syn or the anti aldols under fluoride- or Lewis-acid-promoted conditions. However low yields are obtained due to the formation of the double condensation products or aldols at C-3 site. An alternative six-step synthetic sequence was developed to access the target molecules starting from 2-bromo-phenyl acetaldehyde 20 and 2-methoxy-phenyl acetaldehyde 21. Structural assessment of the aldol products was achieved by stereospecific transformations and 1H NMR nOe experiments.